RepRap.org This is a site where you can find various sources that may help you with building your rep rap printer or even the opportunity to help others with building theirs. The sources you will find include:
wiki- http://reprap.org/wiki/Development RepRap's wiki has many helpful sources and pages that teach you everything you need to know about the printer along with other things about it. It's is a colaborative website which means you are able to create an account under that wiki which then allows you to add to it and make changes to the page as you wish.
RepRapPro http://reprappro.com/